This study is mainly focused on some aspects of the low molecular weight RNA species C and D (or U2 and U1, respectively) in human carcinoma cells, which are among the most abundant of the long-lived, homodisperse, low molecular weight nuclear RNAs. These RNA species seem to be present in at least all vertebrates tested, but their function is unknown. C and D RNA exhibit several interesting characteristics: they appear to be transcribed from multiple-copy genes (102-103 genes/genome), they seem to pass through the cytoplasm for a few minutes shortly after their transcription, have 5' end caps that are very similar to those of eukaryotic mRNAs, and appear to be present in heterogeneous nuclear RNA-protein particles. Our next objective is to study the effect of C and D RNA in cell-free translation systems. The inhibition of C and D RNA synthesis by cycloheximide has been reported by several laboratories. Our results suggest then that it is the maturation, and not the synthesis, of C and D RNA that is affected early during suppression of protein synthesis by cycloheximide. Then, the next goal would be to examine the maturation of RNA species C and D (nucleotide loss, methylation, 5' end cap formation) during inhibition of protein synthesis. Our studies on the effect of glucosamine and galactosamine on the labeling of C and D RNA, while the cellular UTP poll is being depleted, suggest that there might be a minimum of two nuclear UTP pools. This possibility should be pursued further. The metabolic stability of several mammalian low molecular weight RNAs has been determined in growing heteroploid cells. We wish to examine their stability in resting and growing diploid cells. By non-aqueous cell fractionation we have detected three RNA species that apparently have not been described before. One of the is cytoplasmic, and the other two are nuclear. We would like to characterize them.